EP0800285A2 - Method for adjusting the parameters of a receiving apparatus, as well as corresponding receiving apparatus and radio station - Google Patents

Abstract

The parametrisation process uses a channel estimator which incorporates a channel model (KM) and a calculator (RW) implemented advantageously in a digital signal processor. During the training sequence, test data received from a transmitter are stored in digital form (drx) and read out after a delay (M). The memory may be part of the adaptive prefilter (VF) which includes 5 or 6 delay stages (z sup -1) and performs a summation into an antenna datum (zd) for comparison with the output (y) of the channel model. A min. squared error problem-solver (LS) finds the synchronisation position and determines the necessary filter coeffts. (al-an), channel model coeffts. (hl-hn) and delay, while excluding the trivial soln.

Description

The invention relates to a method for parameterizing a receiving device of a radio system with an associated antenna device and with a prefilter and to such a receiving device or a radio station with at least one receiving device.

In a radio system, information is transmitted from a transmitting radio station to a received radio station. This information reaches the received radio station in the form of received signals. Due to various external influences, the received signals reach the receiving radio station over several routes. The signal components corresponding to the different routes arrive at the receiving radio station at successive times. The problem in the receiving radio station is now to equalize these signal components, which may also be influenced by other interference components, to correct the errors and to decode the transmitted information.

Digital Communications", 1989, S.593-595 sind Vorfilter bekannt, die in einer Empfangseinrichtung vor der Detektierung Störkomponenten in den Empfangssignalen unterdrücken, dabei insbesondere Nachbarkanalstörungen. Ein Vorfilter besteht aus Verzögerungsgliedern, in denen die Empfangssignale stufenweise verzögert werden. Die Empfangssignale unterschiedlicher Verzögerung werden jeweils mit einem Filterkoeffizienten bewertet und anschließend aufsummiert. Die Filterkoeffizienten sind jedoch fest vorgegeben und der Vorfilter ist Teil eines Entzerrers, wobei der Detektor als einfacher Schwellwertentscheider ausgebildet ist.From Proakis,

Digital Communications ", 1989, p. 593-595, pre-filters are known which suppress interference components in the received signals in a receiving device prior to detection, in particular adjacent channel interference. A pre-filter consists of delay elements in which the received signals are delayed in steps. The received signals have different delays are each evaluated with a filter coefficient and then added up, but the filter coefficients are fixed and the pre-filter is part of an equalizer, the detector being designed as a simple threshold value decider.

Optimum and sub-optimum detection of coded data distured by time-varying intersymbol interference", IEEE Proceedings 1990, S.1679-84 bekannte Kanalkoeffizienten. Diese in einem Kanalmodell verwendeten Kanalkoeffizienten dienen dazu, verschiedene nacheinander eintreffende Signalkomponenten eines Empfangssignals geeignet zu überlagern.Further parameters are determined within the receiving device for evaluating the received signals. These parameters are from W.Koch,

Optimal and sub-optimum detection of coded data distured by time-varying intersymbol interference ", IEEE Proceedings 1990, p.1679-84 known channel coefficients. These channel coefficients used in a channel model serve to suitably superimpose different signal components of a received signal arriving in succession.

It is also known to feed the antenna data obtained from the received signals by transmission into baseband and analog / digital conversion, and the channel coefficients to a detector which equalizes the antenna data and carries out the error correction. The symbols of the signals reconstructed in the output of the detector are then processed in a decoder, e.g. a Viterbi decoder, decoded.

The GSM System for Mobile Communications", 49. rue Louise Bruneau, F-91120 Palaiseau, Frankreich, 1992, S.231-237, ist es bekannt, sogenannte Trainingssequenzen zu nutzen, um empfangende Funkstationen abzugleichen. Zu vorbestimmten Zeitpunkten sendet die sendende Funkstation eine Sequenz digitaler Daten, die der empfangenden Funkstation bekannt ist, d.h. deren Daten in der empfangenden Funkstation unverzerrt vorliegen.From mobile radio systems, see M.Mouly, M.-B.Pautet,

The GSM System for Mobile Communications ", 49 rue Louise Bruneau, F-91120 Palaiseau, France, 1992, pp. 231-237, it is known to use so-called training sequences to compare receiving radio stations. The transmitting radio station transmits at predetermined times a sequence of digital data which is known to the receiving radio station, ie the data of which are present in the receiving radio station in an undistorted manner.

The object of the invention is to provide a method for parameterizing a receiving device, as well as such a receiving device or radio station in a radio system, which enable adjustable and improved immunity to interference. The object is achieved by the method according to claim 1, and the receiving device according to claim 6 or the radio station according to claim 13. Further developments of the inventive concept can be found in the subclaims.

In a radio system, a receiving device with a prefilter is parameterized in such a way that the filter coefficients of the prefilter are adjustable and, during operation of the receiving device, the prefilter is adaptively adapted to a given immunity requirement, together with the determination of channel coefficients. This makes it possible to cope with changing reception conditions. Such a parameterization of the receiving device proves to be particularly advantageous in radio systems, since the conditions in the radio channel change quickly. Training sequences known in radio systems are suitable, for example, for setting the filter coefficients.

In accordance with an advantageous embodiment of this method according to the invention, received reception signals are converted into digital signals in the receiving device and are gradually delayed in the adaptive pre-filter associated with the receiving device, and the differently delayed received signals are each evaluated and superimposed with filter coefficients. The receiving device also contains a channel model with which the radio channel between the transmitting and receiving radio station can be simulated. The channel model is characterized by channel coefficients by which the channel model is adapted to the real radio channel. The channel model represents, for example, a filter with a finite impulse response. The antenna data and the specific channel coefficients are fed to a detector contained in the receiving device for equalization and error correction of the antenna data.

During a training sequence, the signals represent received test data, which are additionally present undisturbed in the receiving device. Antenna data that can be assigned to the received test data and model variables derived from the channel model fed with the test data are fed to an arithmetic unit. In the arithmetic unit, which also belongs to the receiving device, the Filter coefficients for the suppression of received disturbance variables and the channel coefficients for compensating the transit time differences of different signal components of a received signal are determined. For this purpose an algorithm is used which minimizes the deviation of antenna data of the training sequence and model sizes of the training sequence. The determined filter coefficients and channel coefficients can then also be used to evaluate the signals outside of the training sequence. When processing digital received signals, it is possible to implement a prefilter, channel model and arithmetic unit in a digital signal processor, thereby reducing additional circuitry outlay.

The combination of adaptive prefilter and channel model, as well as the simultaneous calculation of the parameters for the filter coefficients and the channel coefficients in a computing unit, substantially improves the functioning of the receiving device with regard to the reconstruction of transmitted information. The parameters required for setting the receiving device can be determined together using a simple algorithm. It is important to note that the trivial solution with filter coefficients and channel coefficients set to zero is excluded. A corresponding secondary condition must be provided in the algorithm.

Depending on the number of delay elements of the adaptive prefilter, there is an improved interference signal suppression, both for interferers in adjacent channels and in the own channel, in particular sinusoidal interferers. The number of sinusoidal interference that can be completely eliminated corresponds to the number of filter coefficients minus one. The adaptive pre-filter results in a significant improvement in the reception quality, which means that when the radio station is used in a radio system, there is also an increase in system performance, for example in the case of mobile radio systems resulting in a higher density of mobile stations.

According to further refinements of the subject matter of the invention, the algorithm for determining the filter coefficients and the channel coefficients, excluding the trivial solution, is designed in such a way that in the receiving device there are several sets of filter coefficients with which the received test data are each evaluated and then the channel coefficients with a minimal deviation from antenna data and Model sizes can be determined. The solution with the smallest deviation, i.e. the associated filter coefficients and channel coefficients determined for this purpose are selected and used to parameterize the receiving device. This solution reduces the computing effort to the determination of the channel coefficients, while the filter coefficients are selected from a set of known filter coefficients.

An alternative variant is to use the calculation of the smallest squares of errors or a correlation calculation to determine the filter coefficients and the channel coefficients without preselection, and thus to select the filter coefficients and channel coefficients from an infinitely large number of possible values in the case of a greater computational effort, but again with exclusion the trivial solution. The trivial solution, in which the filter coefficients and channel coefficients are set to zero, corresponds to a possible but nonsensical solution. As a result, it is necessary to set one of the filter coefficients or the channel coefficients to a non-zero value.

According to a further advantageous embodiment of the subject matter of the invention, prior to the final determination of the filter coefficients and the channel coefficients, the test data received is synchronized with the test data processed in the channel model. By an unpredictable Runtime of the received signals of the training sequence between transmitter and receiver, the time of arrival of the received test data in the receiving device cannot be predicted with complete certainty. In order to ensure the start of the training sequence and an effective calculation of the filter coefficients and channel coefficients without the disruptive influence of insufficient synchronization, a delay is therefore calculated with which the received signals are applied in the receiving device. The delay can be determined, for example, by minimizing the deviation at several positions in the data stream of the antenna data and selecting the optimal solution, which corresponds to the synchronization. This delay is then used outside of the training sequence.

In the remaining claims, a radio station is specified, the receiving device of which is designed to carry out the parameterization. This radio station is advantageously used in radio systems which are operated in time slot multiplex and the parameterization is redetermined for each individual time slot. An example of a radio system operated in time division multiplexing is mobile radio systems (GSM, GSM-like) or cordless communication systems (DECT), the radio station being operated as a base station or mobile station. The receiving device or radio station according to the invention and the method according to the invention particularly meet the special conditions of a mobile radio system, since the mobility of communication terminals results in changing propagation conditions, to which the parameterization of the receiving device can be adapted accordingly.

The subject of the invention is to be explained in more detail below with the aid of drawings.

FIG 1

ein Blockschaltbild einer Funkstation,

FIG 2

ein Blockschaltbild eines Kanalschätzers während der Parametrierung,

FIG 3

ein Blockschaltbild der Empfangseinrichtung während des Empfangs mit zuvor bestimmten Parametern außerhalb der Trainingssequenz.

Show

FIG. 1

a block diagram of a radio station,

FIG 2

a block diagram of a channel estimator during parameterization,

FIG 3

a block diagram of the receiving device during reception with previously determined parameters outside the training sequence.

1 shows the receiving device EE and the associated antenna device AE of a radio station. This radio station is part of a radio system and receives reception signals rx from a transmitting radio station of this radio system. The radio system is, for example, a GSM mobile radio system in which the radio station shown in FIG. 1 represents a base station. Base stations are each connected to handsets via an air interface, which represent the transmitting radio station, for example. The reception case for the base station is shown below, nevertheless there is usually a two-way traffic relationship, i.e. the base station also has a transmitter. The receiving device of the mobile part can also be designed in accordance with the invention.

From the received signals rx received in the antenna device AE, e.g. digital signals drx are generated by transmission in the baseband and subsequent analog / digital conversion and are fed to an equalizer which is arranged within the receiving device EE. It should be noted that the antenna data z and the coefficients c, h to be calculated below represent complex values if the baseband conversion differs in in-phase and quadrature components.

The equalizer contains a channel estimator KS and a detector DT. The digital signals drx serve as input signals for the channel estimator KS, which is connected to the detector DT and feeds it antenna data z derived from the digital signals drx and furthermore channel coefficients h determined in the channel estimator KS.

The detector DT carries out an equalization and error correction of the antenna data z with the aid of the channel coefficients h and generates symbols s which are supplied to further devices of the receiving device EE, in which decoding and, if necessary, further processing steps are then carried out. The symbols s represent the reconstructed signals rx processed by equalization and error correction.

The functioning of the channel estimator KS during the parameterization is explained in FIG. The devices KM, RW contained in the channel estimator KS are advantageously implemented in a digital signal processor. Appropriate algorithms can be used in the digital signal processor in addition to solving the problem of the smallest squares of errors, corresponding delays of data elements and a simulation according to the channel model KM.

The parameterization takes place while a training sequence is being received. During this training sequence, the test data d are transmitted from a transmitting radio station to the receiving radio station shown in FIG. Due to multipath propagation, interference and delay, the received signals rx arrive at the receiving radio station and are available to the channel estimator KS as digital signals drx.

These digital signals drx are stored in a memory element and output delayed by a delay M. The storage element is, for example, part of an adaptive pre-filter VF. The pre-filter VF contains several (eg 5 or 6) delay elements z ^-1 , in which the digital Receive signals are gradually delayed. The digital signals drx are then each evaluated by filter coefficients a and then summed up, the summation giving an antenna date zd of the training sequence. Successive reception signals rx thus result in the antenna data zd of the training sequence.

The test data d known in the receiving device EE are fed to a channel model KM. This channel model KM consists of delay elements z ^-1 , which are arranged in a chain. The test data d pass through these delay elements z ^-1 . The undelayed test data d and the delayed test data d present at the output of each delay element z ^-1 are each evaluated with a channel coefficient h and then summed up to a model variable y. In this channel model KM, multipath propagation is simulated, signal components arriving one after the other being superimposed to form a common signal. In mobile radio systems, 3 to 4 delay elements z ^{-1 are} sufficient to compensate for the multipath propagation. The model variables y are the output variables of the channel model KM.

Furthermore, the channel estimator KS contains an arithmetic unit RW which compares the antenna data zd of the training sequence and the model sizes k and determines the deviation e of the two values. The deviation e is supplied within the arithmetic unit RW to a unit LS which determines the filter coefficients a, channel coefficients h and the delay M required for a minimum deviation e.

The delay M is first determined for parameterization. The unit LS solves the problem of the smallest squares of errors at several positions of the received data stream, which is formed by the antenna data and the training sequence. The position with the smallest quadratic error represents the synchronization position. This also determines the delay M, which follows when processing the received signals rx is also used outside the training sequence for the same time slot. When solving the problem of the least square error, the secondary condition is observed that not all filter coefficients a and channel coefficients h may be equal to zero. For this reason, for example, one of these values is preset to a non-zero value.

This procedure results in the synchronization and the determination of the filter coefficients a and channel coefficients h at the same time. When solving the problem of the least squares of errors, the deviation e can advantageously be normalized by the sum of the squared channel coefficients h, as a result of which the synchronization can be further improved. Instead of solving the problem of least squares, other suitable algorithms can also be used which bring about a minimization of the deviation e. The channel coefficients h, filter coefficients a and the delay M determined by the arithmetic logic unit RW are then also used outside the training sequence to improve the reception of the receiving device EE.

FIG. 3 shows the reception and further processing of the received signals rx outside the training sequence. The channel estimator KS picks up the digital signals drx and delays them in accordance with the previously determined delay M before they are delayed in the adaptive pre-filter VF and are superimposed on the antenna data z by the determined filter coefficients a. This antenna data z is fed to the detector DT through the channel estimator KS. Furthermore, the determined channel coefficients h are also transmitted from the channel estimator KS to the detector DT.

This detector DT can then perform the equalization and error correction of the antenna data z and generates the symbols s. The receiving device EE according to the invention shows an improved suppression of interference signals by the combination of pre-filtering and consideration of runtime differences of signal components is achieved in a single algorithm. The complexity of the adaptive prefilter, for example the number of delay elements z ^-1 , plays a role in the effectiveness of the radio station according to the invention and the method according to the invention.

Claims (16)

Method for parameterizing a receiving device (EE) in a radio system, in which receive signals (rx) are received, digitized, fed to a pre-filter (VF) by an assigned antenna device (AE), and then equalized and error-corrected,
characterized, that the pre-filter (VF) is designed as an adaptive pre-filter (VF), and a simultaneous setting of filter coefficients (a) of the pre-filter (VF) and channel coefficients (h) of a channel model (KM) takes place during reception. The method of claim 1, wherein by the receiving device (EE) - digital signals (drx) derived from the received signals (rx) are delayed in the adaptive prefilter (VF), the differently delayed digital signals (drx) are each evaluated with the filter coefficients (a) and superimposed on antenna data (z, zd), the antenna data (z) and the channel coefficients (h) determined in the channel model (KM) and provided to take into account the multipath propagation of the received signals (rx) are fed to a detector (DT) for equalization and error correction of the antenna data (z), where during a training sequence with test data (d): - Model variables (y) and the antenna data (zd) assignable to the received test data (d) are fed to an arithmetic unit (RW), the model variables (y) being fed from the undistorted test data (d) present in the receiving device (EE) Channel model (KM) derived, - in the calculator (RW) - The filter coefficients (a) to suppress received interference and - The channel coefficients (h) to compensate for the transit time differences of different signal components of a received signal (rx) can be determined simultaneously with an algorithm, which is provided to minimize the deviation (e) from antenna data (zd) of the training sequence and model sizes (y) of the training sequence, and these specific filter coefficients (a) and channel coefficients (h) are provided for evaluating the received signals (rx) outside the training sequence. Method according to claim 2, in which the algorithm for determining the filter coefficients (a) and the channel coefficients (h) is designed to the exclusion of the trivial solution (a = 0; h = 0), - that the received test data (d) are evaluated with several predetermined sets of filter coefficients (a) and the channel coefficients (h) are determined with a minimal deviation (e) from antenna data (zd) and model variables (y), and - The set of filter coefficients (a) in which the deviation (e) of antenna data (zd) and model sizes (y) is the smallest, and the associated specific channel coefficients (h) is selected. Method according to claim 2, in which the algorithm for determining the filter coefficients (a) and the channel coefficients (h) is designed to the exclusion of the trivial solution (a = 0; h = 0), that the deviation (e) of antenna data (zd) and model sizes (y) is minimized by calculating the smallest squares of errors. Method according to one of claims 2 to 4, in which, prior to determining the filter coefficients (a) and the channel coefficients (h) by determining a delay (M), a synchronization of the received test data (d) with the im Channel model processed test data (d) is made and the delay (M) for evaluating the received signals (rx) is also provided outside the training sequence. Receiving device (EE) in a radio system, with an assigned antenna device (AE) for receiving received signals (rx), - with a pre-filter (VF) for delaying digital signals (drx) derived from the received signals (rx), - To evaluate the differently delayed digital signals (drx) each with filter coefficients (a), and to superimpose them on antenna data (z, zd), with a detector (DT) for equalization and for error correction of the antenna data (z) by evaluating the antenna data (z) and in a channel model (KM) certain channel coefficients (h) provided to take into account the multipath propagation of the received signals (rx), characterized, that means (RW) for simultaneously setting the filter coefficients (a) of the pre-filter (VF) and the channel coefficients (h) of the channel model (KM) are provided and the pre-filter (VF) is therefore adaptive. Receiving device (EE) according to claim 6, - With an arithmetic unit (RW) for determination - The filter coefficient (a) to suppress received interference and - The channel coefficients (h) to compensate for the transit time differences of different signal components of a received signal (rx) using an algorithm for minimizing the deviation (e) from antenna data (zd) the training sequence and model sizes (y) of the test data (d) present in the receiving device (EE) during a training sequence. Receiving device (EE) according to claim 7, which also provides for the evaluation of the received signals (rx) with the determined filter coefficients (a) and channel coefficients (h) outside of the training sequence. Receiving device (EE) according to one of claims 7 or 8, in which the adaptive pre-filter (VF) provides for the evaluation of the signals (rx, drx) with several predetermined sets of filter coefficients (a) during the test sequence and the arithmetic unit (RW) provides for the determination of the channel coefficients (h) in such a way that the set of filter coefficients (a) with which the deviation (e) from antenna data (zd) and model sizes (y) is the smallest, and the associated determined channel coefficients (h) can be selected excluding the trivial solution (a = 0; h = 0). Receiving device (EE) according to one of Claims 7 to 9, in which the arithmetic unit (RW) during the test sequence determines the filter coefficients (a) and the channel coefficients (h) with a minimal deviation (e) from antenna data (zd) and model sizes (y) according to the least squares method, excluding the trivial solution (a = 0; h = 0). Receiving device (EE) according to one of claims 6 to 10, in which the arithmetic unit (RW) provides for determining a delay (M) for the synchronization of the received test data (d) with the test data (d) processed in the channel model, independently or depending on the determination of the channel coefficients (h) and filter coefficients (a) and the adaptive pre-filter (VF) provides the delay (M) in the evaluation of the signals (drx, rx) for synchronization, even outside the training sequence. Receiving device (EE) according to claim 10, in which the synchronization is effected in that a determination is made at several positions of the antenna data (zd) the channel coefficients (h) and filter coefficients (a) is made and the solution with the smallest deviation (e) is selected. Radio station with a receiving device (EE) according to one of claims 6 to 12. Radio station according to claim 13, which is operated in time slot multiplex and which provides for the determination of the parameters (a, h, M) for each time slot. Radio station according to one of claims 14, which is operated as the base station of a mobile radio system. Radio station according to one of claims 14, which is operated as a mobile station of a mobile radio system.

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